Tracking flares



April 1958 A. c. LOEDDING 2,829,596

TRACKING FLARES Filed Dec. 17, 1954 uh. m...,- m. nv- Hm.

I -PRESSURE ALUMINUM Fo/ SENSITIVE ADHES/VE INVENTOR Y flfi edZaeridzzzg his ATTORNEY 9 TRACKING t nn tus;

. Alfred. C. Loedding, Princeton, .N."J., assignor 't o Un excelledChemical Corporation, New York, N. Y., a corporation ofNew YorkApplication December 17, 1954; Serial No. 476,017 f slelaims'. c1.10z s7invention relates to flares and more particularly to a tracking flareforguided'missiles and the like. i I

The invention provides a flare which is relatively small in size and itscharge may therefore be fabricated in 1 standard pelleting machines,said charge producing a brilliant substantially smokeless flame clearlyvisible from a distance ofupto 15,000 feet in clear daylight,having'high combustion stability during required burningduration ofbetween 15-'l9 seconds, and which isstorable for long periods of time up.to 5 years and even longer. The low-cost, simple construction providesgreat ruggedness andycertainty of operation necessary for use inconnection with missiles.

The invention further provides a flare whose electrical l ignitionsystem is simple and reliable, anda safety device which is provided toprevent preignition during storagehandling;

j The novelflare consists essentially of a tubular housing of vulcanizedfibre or the likehaving one of its ends closed and its other end sealedby a disc of cardboard or other lightweight material that is easilydestructible.

A. pellet of a solid-fuel charge having all its sides or all n butone ofits sides inhibited, is inserted into the housing and cemented thereinwitha layer of elastic material. Thepreferably uninhibited surface ofthe charge facing the open end'of the housing is covered by a layer ofignitionpowderpaste and the cardboard disc tightly pressed thereagainstto expel anyair which could cause rupture at higher altitudes. In thepreferred embodiment, an electric match is embedded in the ignitionpowder paste and the leads connecting the matchwith a source'of electricenergy are led along the periphery of the housing to provide a largecontact surface. When i in storage, the' leads are short-'circuitedby alayer of metallic-foil which is removed only before the flare is ;;Thepelletf consists of a solid-fuel charge of theme-, chanical mix varietywith a preferred composition of about by weight aluminum, by weight of.an-asphalt resin, and about 75% by weight of an oxidizing agent. Theoxidizing agent preferably consists of ammonium perchlorate. To achievethe desirable red color and hence long wavelength for tracking purposes,7

non-hygroscopic'strontium nitrate is added.

U ed States Pur O" 2,829,596 Patente l? 3 1 2 indicate. similarelements, andth'e invention will be final ly pointed out in the appendedclaims.

In theidrawings, v Fig.1 'is an enlarged perspectiveview of theassembled flare partlybroken away to show the igniton system and thetwo'leads to a source of electric energy;

Fig. 2 is afront view of the novel flare;

Fig.3 shows an attachment at the nozzle end of a guided missile or the eto receive and retain the flare casing;

Fig. 4 shows a double electric match for ignition of the solid-fuelcharge in the flare;

': mounted atthe nozzle end thereof 'askew and exteriorly as an example;and t Fig. 7 is anenlarged view of the nozzle end of the missile shownin Fig. 6.

Referring now in more detail to the illustrated embodi-' ment, there isshown in Fig. 1 a tubular casing 10 made preferably of vulcanized fibreand having one end closed by a disc 11 of like material. Pellet 12representing the solid-fuel charge is provided with a layer' ofinhibiting material on all except one of its surfaces and is cemented tothe inner walls of casing 10 and to the disc 11 by a layer of elasticmaterial. However, also this ignition surface could be inhibited withthe prime coat only, because the ignition powder paste, when ignited,would be adequate to burn through this coating. In manufacture, theentire exteriorof pellet 12 may be inhibited with the prime coat and thethin 'film'of inhibiting material removed from the surface facing theopen end of casing 10.

A layer of ignition powder paste 14, such as for example a black powderpaste, is applied to the uninhibited surface of pellet 12 and aspecially fabricated double electric match 15 using a pair of singlematches, such as those manufactured by the Atlas Powder Company, isembedded in paste;14.' A cardboard disc 16 is air-tightly pressedagainst the layer of paste 14. The positive and negative leads 17, 18from electric match 15 are led through slots 19, 20 at the left-hand endof casing or tube 10, along the periphery thereof, through slots 21, 22at the right-hand end of casing 10 and are then bent into the circularrecess23 above disc 11, as shown in Fig. 2.

A strip 24 of pressure-sensitive material, covering a thin band 25 ofaluminum foil, is applied to the periphery of casing 10 so that thealuminum foil 25 short-circuits both terminals leading to the electricmatch 15.

When the flare is ready for use, the adhesive strip 24 is [be providedat the nozzle end 28a of a guided missile shown in Figs. 6 and 7. Theattachment comprises two substantially parallel resilient metallicconductors 29, 30

having their free ends 31, 32 bent inwardly to retain the flare byacting against the left-hand end thereof, and a ,Further. features andadvantages "of the novel flare will beipointed out in the course of thefollowing detailed description of one preferred embodiment thereof,taken in conjunction ,with the description of the figures in the acpairof lips 31a, 32a made of conductive material fitting into slots 21, 22at the right-hand end of tube 10 to in the wires may be shaped as shown,around the edges of tube 10, through slots 19-22 and into recess 23, asthey are sufliciently rigid to prevent the electric match 15 from beingblown out of the flare during considerable forward speed of the missile.Those portions of leads 17, 18 passing through ignition powder paste 14and up to slots 19, 20 are preferably electrically insulated by sprayingor the like. The match 15 ignites the layer 14 of ignition powder pastewhich in turn uniformly ignites the entire uninhibited surface of pellet12.

The vulcanized fibre casing may blister slightly internally and showtraces of slight charring, but will adequately resist the intense heatduring combustion of pellet 12. Disc 11 is pressed into tube 10 andretained therein by frictional or mechanical bonding. However, thecasing 10 may be manufacturedwith one end closed, the arrangement with aseparate disc 11 being shown to indicate that the casing may be cutfroma longer tubular body for ease of manufacture and lower cost The layer13 of elastic cement inside tube 10 and on the inner side of disc 11also securely seals said disc in the tube and prevents pellet 12 frombeing ejected from the tube under high axial acceleration forces. Thiselastic material may be the same as the secondary inhibiting coating ofpellet 12. In manufacture, the pellet 12 having all but one of itssurfaces inhibited to assure end burning (cigarette type), is pressedinto tube 10 after the elastic cement 13 has been applied to the innerwall of disc 11 and the pellet will then distribute the cement 13 alongits contact surface with casing 10 and disc 11, thereby tightly sealingthe same into the tubular body 10 and against the inner wall of disc 11.

The layer of ignition powder paste-14 along the uninhibited surface ofpellet 12 is desirable to uniformly ignite the uninhibited surface ofthe pellet and tov minimize the amount of entrapped air between disc 16and pellet 12. Such air could cause serious blowout at certain altitudesdue to the pressure difference between atmospheric air and thatentrapped in the flare.

The pellet 1.2 is actually retained during combustion thereof by thelayer of elastic cement, which may be the secondary inhibiting material13 and also due to the fact that the flare is preferably mounted in amanner shown in Figs. 6 or 7, i. e. with its longitudinal axis at anangle to the axis of the guided missile, target drone, boat or any otherobject to be tracked.

. This positioning at an angle also permits observation of a largerportion of the flame 34 during burning of the charge, when viewed fromthe launching point, as not only the tail of the flame 34 but also aportion of its side will be observable. Also, by positioning thetracking flare close to the inner nozzle wall 28a of the missile, theflames could destroy the disc 16 and ignite the layer of ignition powderpaste 14 without any electrical matches. This is possible due to theextremely short housing 10 of the noval flare, a configuration entirelynovel in this art, adding desirable ruggedness to the structure. Forexample, the outside diameter of the housing 10 is only 1 inch, and thelength thereof 1 /4 inch.

In Fig. 7,-the inclination of flares 10 with respect to the axis ofmissile 2 8 is somewhat exaggerated for better illustration. Also, whileflares 10 are shown outside the nozzle wall 28a, they are preferablymounted in suitable grooves or in a circular recess in said wall 28a.The 6-8 inch flame may be protected by a transparent housing against thewind at high speeds and to obtain a greater visual effect. The visualeffect could be further improved by mounting the flare into a coneacting in a manner similar to that of the reflector for the bulb in aflashlight.

The novel composition of the pellet insures a burning rate ofapproximately 0.05-inch per second or less for a total time of about15-19 seconds and observation of the flame at a distance of 15,000 feetin clear daylight with naked eye. The brilliancy of the flame isachieved by addition of fine aluminum powder in the approximateproportion of 10% by weight. While magnesium and zirconium may also beused to add brilliancy to the flame, the use of these elements should beavoided because of their high afiinity toward ammonium perchlorate, theoxidizing agent present in the pellet mixture. Other advantages of thealuminum powder are ease of ignition, combustion stability, greatbrilliancy during combustion and good storage life.

A preferred composition of the pellet is as follows:

Percent by weight Aluminum powder 10 Asphalt resin 15 Ammoniumperchlorate 37.5 Strontium nitrate 37.5

While the percentage of aluminum powder in the mixture may be slightlyvaried, a pellet containing more than 15% of aluminum powder is notnecessary and does not warrant the reduction in safety. It is believedthat the oxide layer surrounding each aluminum particle is partlyremoved during intimate mixing and grinding of the mixture and that thealuminum may react with the oxidizing agent. This is avoided bypreferably first mixing and/ or grinding the asphalt resin with theoxidizing agents and then afterward adding aluminum powder for thoroughmixing only with little or no grinding action.

Another mode of preventing the aluminum powder from reacting with theoxidizing agent is to coat the aluminum particles with a suitable oil,such as linseed oil, or with a suitable wax. Calcium stearate may beadded in quantities between /2--1% by weight. This substance also servesas a coating and a lubricant especially for aluminum particles andreduces friction of aluminum during the pelleting operation.

The asphalt resin serves as both the fuel component and binder in themixture, as more fully described in my copending application for LettersPatent of the United States, filed under Serial No. 454,209 on September3, 1954. This resin is a black, odorless substance characterized byconchoidal and lustrous fracture. It is a low penetration, highsoftening point resin (with a softening point between 176 and F.),derived from petroleum crude oil by precipitation with solvent. The lowvolatility (high flash) of this resin makes it suitable for hightemperature application. It is low in saturated hydrocarbons, high inresins and contains no free carbon. Its sulphur content is very low,only about 1.4% by weight.

The typical chemical composition of the resin is:

Percent Asphaltenes 8.0 Resins 89.0 Saturated oils 3.0

The resin is readily soluble in coal tar or petroleum naphthas. It isgenerally compatible with petroleum oils, asphalts, pitches, vegetableand fatty oils, alkyd resins and several rubber types. It has heretoforebeen used in adhesives, battery boxes, battery sealing compounds, forconcrete Waterproofing, in floor tiles, in mastic manufacture, papercoating emulsions, in rubber compounding as a tackifier, etc.

The main advantage of the resin lies in that it serves as the fuelcomponent and the binder at the same time. Thus, no inert binders arerequired.

When it is desired to have only infra-red light waves actuating trackingdevices, aluminum powder could be eliminated and the percentage ofasphalt resin increased accordingly, but should not exceed 30% byweight.

Ammonium perchlorate is a very active oxidizing agent and its presencein the charge is essential to insure combustion stability. The activityof ammonium perchlorate is believed to be increased by the presence ofaluminum powder.

tain at least 25% of ammonium perchlorate, based on The oxidizing agentin the charge should con- The mixing of the charge ingredients ispreferably achieved in the Entoleter (trademark) which insures uniformmix for any quantity of the mixture. 7

While I have described one at this time preferred embodiment of myinvention, I do not desire to be limited 1 to the exact details thereof,but only by the scopeof the appended claims.

I claim:

1. In a tracking flare having a tubular body with an i open end and aclosed end: a solid fuel charge in said sealing said open end of saidbody, and an electric match embedded in said ignition powder paste, saidmatch having two conductive leads extending along the periphcry of saidbody.

2. The structure defined in claim 1, wherein said solidfuel charge is amechanically mixed composition comprising about 10% by weight ofaluminum powder,

about by weight of a petroleum base resin and about 75% by weight of anoxidizing agent, said oxidizing agent consisting of approximately equalproportions of ammonium perchlorate and strontium nitrate.

3. The structure defined in claim 1, wherein said solidfuel charge is a.mechanically mixed composition comprising about 25 by weight of apetroleum base resin and about 75% by weight of an oxidizing agent, saidoxidizing agent consisting of approximately equal proportions ofammonium perchlorate and strontium nitrate.

4. In a tracking flare having a tubular body with an open end and aclosed end: a solid fuel charge in said body consisting of a fuelcomponent and an oxidixing agent, said oxidizing agent containing atleast 25 percent by weight based on the weight of the charge of ammoniumperchlorate and said solid fuel component containing between 5 and 30percent by weight based on the weight of the charge of a petroleumresin, a layer of ignition powder paste applied to said charge on itssurface facing said open end of said body, a closure member tightlyapplied against said layer of ignition powder paste for sealing saidopen end of said body, an electric match embedded in said ignitionpowder paste, said match having two conductive leads extending along theperiphery of said body, and a pressure sensitive tape embodying aconductive element removably applied to the periphery of said body forshort-circuiting said leads during storage and handling.

5. In a missile having a longitudinal axis and a nozzle at the rear endthereof, the combination of a tracking flare including a tubular bodywith an open end and a,

closed end, a solid fuel charge in said body consisting of a fuelcomponent and an oxidizing agent,'said oxidizing agent containing atleast 25 percent by weight based on the weight of the charge of ammoniumperchlorate and said solid fuel component containing between 5 and 30percent by weight based on the weight of the charge of a petroleumresin, a layer of ignition powder paste applied to said ,charge on itssurface facing said open end of said body, a closure member tightlyapplied against said layer of ignition powder paste for sealing saidopen end of said body, an electric match embedded in said ignitionpowder paste, said match having two conductive leads extending along theperiphery of said body, and an attachment for said flare supported atsaid rear end of said missile, said attachment including at least tworesilient conductive members conductively contacting said leads and asource of electrical energy connected with said conductive members.

6. In a missile having a longitudinal axis and a nozzle at the rear endthereof, the combination of a tracking flare including a tubular bodywith an open end and a closed end, the diameter of said body beinggreater than the length thereof, a solid-fuel charge in said bodyconsisting of a fuel component and an oxidizing agent, said oxidizingagent containing atleast 25 percent based on the weight of the charge ofammonium perchlorate and said solid fuel component containing between 5and 30 percent based on the weight of the charge of a petroleum resin, alayer of ignition powder paste applied to said charge on its surfacefacing said open end of said body, a closure member tightly appliedagainst said layer of ignition powder paste for sealing said open end ofsaid body, and means at said rear end of said missile for supportingsaid tracking flare in such manner that said body is inclined withrespect to said axis of said missile and said open end thereof is closerto said axis than said closed end, whereby said ignition powder pastemay b ignited by the gases escaping through said nozzle of said missile.

References Cited in the file of this patent UNITED STATES PATENTS

